Plastic containers are easy to form, can be inexpensively produced, and have, therefore, been widely used in a variety of applications. Specifically, olefin resin containers directly blow-formed in the shape of a bottle and having an inner surface formed by using an olefin resin such as low-density polyethylene, have been favorably used as containers for containing viscous slurry or paste-like liquid contents such as ketchup and the like from such a standpoint that the contents can be easily squeezed out.
Further, the bottles containing highly viscous liquid contents are, in many cases, stored in an inverted state so that the contents can be quickly discharged or can be all used up to its last drop without remaining in the bottles. When the bottles are inverted, therefore, it is desired that the viscous contents do not adhere or remain on the inner wall surfaces of the bottles but fall down quickly.
As a bottle for satisfying the above requirements, for example, a patent document 1 is proposing a bottle of a multilayered structure in which the innermost layer comprises an olefin resin having an MFR (melt flow rate) of not less than 10 g/10 min.
In the above bottle of the multilayered structure, the innermost layer has excellent wettability for the oily contents. Therefore, if the bottle is inverted or is titled, the oily content such as mayonnaise or the like falls down spreading over the surface of the innermost layer and is completely discharged without adhering or staying on the inner wall surface (surface of the innermost layer) of the bottle.
As bottles for containing viscous non-oily contents in which plant fibers are dispersed in water like ketchup, patent documents 2 and 3 are proposing polyolefin resin bottles having an innermost layer that is blended with a saturated or unsaturated aliphatic amide as the lubricant.
The above patent documents 1 to 3 are all concerned to plastic containers having improved slipping property to the contents relying upon the chemical compositions of the thermoplastic resin compositions forming the inner surfaces of the containers, and are achieving slipping properties improved to some extent. Due to limitation on the kinds of the thermoplastic resins and on the additives, however, limitation is also imposed on improving the slipping properties, and striking improvements have not been achieved yet.
In recent years, further, there has been proposed a container having an inner surface that is a liquid-permeable surface, i.e., having a surface that is a liquid-permeable surface on the side that comes in contact with the content (patent document 4). In the above container, a film of a liquid is formed on a portion that comes in contact with the liquid content in the container, the film of the liquid exhibiting very improved slipping property to the liquid content such as ketchup, sauce, mayonnaise or the like.
In the containers of this kind, however, there still remains a problem in regard to how to thinly, uniformly and efficiently form the film of the liquid to improve slipping property to the contents.
A generally employed means comprises, for example, forming a container, spraying a liquid onto a portion of the container to where the content comes in contact to form a film of the liquid thereon and, thereafter, filling up the content. This means, however, necessitates the step of forming the liquid film prior to filling the content causing, therefore, a decrease in the productivity. Further, if it is attempted to uniformly form the liquid film in the container by the above means, it becomes necessary to spray the liquid in unnecessarily large amounts. As a result, liquid reservoirs tend to form in the container causing a large dispersion in the thickness of the liquid film.
The present applicant has is proposed a means of forming a liquid film by mixing a liquid into a resin that forms the inner surface of a container (JP-A-2013-23468. PCT/JP2014/052879). According to this method, there is no need of providing the step of forming the liquid film prior to filling up the content and, therefore, the productivity is satisfactory. The liquid film, however, is formed on the inner surface of the container as the liquid bleeds out from the blend of resin that is forming the inner layer. Therefore, the thickness of the liquid film often becomes considerably small, and it is difficult to reliably control the thickness of the liquid film.